Appendages of very young mouse and hamster pups will be amputated at different levels and examined through several weeks for cellular dedifferentiation, RNA and DNA synthesis, and mitotic activity. In salamander limbs, the extent of these cellular activities can be correlated to the normal or insufficient influences of injury, nerves, and the wound epidermis. Similar correlations should be possible with mammalian appendages and will provide insight into why mammalian limbs normally do not regenerate. In an effort to obtain regeneration, mouse and hamster pup digits will be experimentally treated with mouse Ringer's solution, 0.9% CaCl2, or wound dressings similar to treatments resulting in digit regeneration in mice and fingertip regeneration in children. In addition, aneurogenic mouse and hamster limbs will be obtained by grafting limb buds to chick chorioallantoic membranes. Segments of these limbs will be grafted to other chick chorioallantoic membranes to test for regeneration. Aneurogenic limbs of salamanders without nerves and preliminary evidence indicates aneurogenic limbs of mice and hamsters also show a regeneration-like response.